Cross-ply composite flywheels are described in U.S. Pat. No. 3,788,162 (Rabenhorst et al.) and U.S. Pat No. 4,102,221 (Hatch). A flywheel including a cross-ply composite core and a composite rim is described by Hatch in co-pending U.S. Patent Application, Ser. No. 955,830, filed Oct. 30, 1978, now U.S. Pat. No. 4,207,778 and assigned to the assignee hereof. The present invention is neither disclosed nor suggested by the above-cited patents and Hatch application, which are incorporated herein by reference.
In greater detail, the Hatch application describes a preferred flywheel (referred to therein as a "circumferentially reinforced cross-ply composite flywheel" and referred to hereinafter as the "Hatch Flywheel"), which comprises a cross-ply composite center portion comprising a plurality of fiber-containing layers. The fibers of each layer are parallel to each other, extend in radial and chordal directions, and are each disposed in a matrix of binder material. The fibers of each successive layer are oriented at a single predetermined angle of between approximately 70.degree. and approximately 110.degree. to the fibers of the preceding adjacent layer such that at least four of the fiber-containing layers are disposed between any two layers in which the fibers of both such layers (i.e., the two last-mentioned layers) extend substantially parallel to each other. A means is included for radially outward transfer of centrifugal loading from the radially outermost chordal fibers of each layer of the central cross-ply composite portion. The load-transfer means is an outer rim portion contiguous with the cross-ply composite central portion and of an axial thickness at least as great as that of the central portion. The outer rim portion comprises a multiplicity of circumferentially-extending fibers disposed in a matrix of binder material. The density-to-stiffness ratio of the rim portion is substantially less in value than the density-to-stiffness ratio of the cross-ply composite central portion.
The Hatch application further discloses such a flywheel wherein the cross-ply composite central portion is in compression in a radial direction and the rim-portion fibers are in tension. Although that application does not contain an express written description of the numerical ratio of the radius of the central portion to the outer radius of the rim portion, such numerical ratio appears to be greater than 0.92 in FIGS. 2-3 thereof.
In an article by E. L. Lustenader and E. S. Zorzi titled "A Status of the `Alpha-Ply` Composite Flywheel Concept Development," proceedings of the Society for the Advancement of Material and Process Engineering, Volume 23, Pages 712-727 (1978), there is described a rim-core composite flywheel wherein the core is an E-glass disk having an outside diameter of 29 inches and a circumferential wrap of Kevlar tape. Since the overall diameter of that flywheel is 30 inches, the radii ratio is about 0.9667.